Epicyclic gear systems

ABSTRACT

An epicyclic gear system (A, B), which is highly compact, yet capable of transferring substantial torque, includes a sun gear ( 2, 62 ), a ring gear ( 4, 64 ) around the sun gear, and planet gears ( 6, 8, 66, 68 ) organized in two rows between the sun and ring gears. In addition, the gear system has a carrier ( 10, 70 ) provided with one or two flanges ( 14, 72, 74 ) and flexible pins ( 20, 22, 80, 82 ) around which the planet gears revolve. The planet gears are mounted on the pins in a double cantilever arrangement to improve the mesh with the sun and ring gears and achieve better load distribution.

CROSS REFERENCE TO RELATED APPLICATIONS

This application derives and claims priority from U.S. provisionalapplication 60/442,883 filed 27 Jan. 2003 for the invention of G. Foxentitled “Epicyclic Gear System” and from International ApplicationPCT/US2004/002157 (WO 2004/067998), filed on 27 Jan. 2004, by the TimkenCompany.

TECHNICAL FIELD

This invention relates in general to gear systems, and more particularlyto epicyclic gear systems.

BACKGROUND ART

The typical epicyclic or planetary gear system basically has a sun gearprovided with external teeth, a ring gear provided with internal teeth,and several planet gears located between the sun and ring gears andhaving external teeth which mesh with the teeth on the sun and ringgears. In addition to its gears, the typical system has a carrier towhich the planet gears are coupled. Typically the sun gear, the ringgear, or the carrier is held fast, while power is delivered to and takenfrom the remaining two components, and thus power is transferred throughthe planetary system with a change in angular velocity and an inversechange torque. However, in some epicyclic systems all three rotate.

The sun and ring gears for all intents and purposes share the sameaxis—a central axis—while the planet gears revolve about radially offsetaxes that are parallel to the central axis—or at least they should be.Often the offset axes and the central axis are not parallel, and as aconsequence the planet gears skew slightly between sun and ring gears.This causes excessive wear along the teeth of the planet, sun and ringgears, generates friction and heat, and renders the entire system overlynoisy.

The problem certainly exists in straddle-designed planetary carriers.With this type of carrier the pins on which the planet gears rotateextend between two carrier flanges in which the pins are anchored attheir ends. The carrier experiences torsional wind up which causes onecarrier flange to rotate slightly ahead of the other flange and producea poor mesh between the planet gears and the sun and ring gears. Eachpin at its ends in cross section should possess enough shear area andsection modulus to withstand the shear forces and bending momentsexerted on the pin by the flanges.

Another type of epicyclic gear system utilizes a single flange carrierand flexible pins anchored in and projected from the flange. In thisarrangement the single carrier flange is offset axially from planetgears, and the carrier pins project from that flange into—and indeedthrough—the planet gears. Each carrier pin has one end anchored in thecarrier flange and at its other end is fitted within a sleeve whichreturns back over the pin, yet is spaced radially from the pin, tosupport the planet gear—a double cantilever so to speak. U.S. Pat. No.3,303,713 to R. J. Hicks shows such a double cantilevered arrangement.But the sleeves occupy space which could otherwise be utilized toenlarge the pin diameter, and when an antifriction bearing is interposedbetween the sleeve and the planet gear that is around the sleeve, evenless space is available for the pin.

Essentially, the double cantilever, with a sleeve interposed between aplanet gear and the pin about which the gear rotates, reduces the crosssection of the pin and of course the shear area and section modulus.This can reduce the torque capacity of the system, so frequently morepins are added to increase the available total cross-sectional area ofthe pins and regain some of the lost torque capacity. Using more pinsnecessarily spaces the peripheries of the planetary gears closertogether. Sometimes the number of pins required to achieve the requiredtorque capacity will result in interference between the planetary gears.

DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view, partially broken away and in section, ofan epicyclic gear system constructed in accordance with an embodying thepresent invention;

FIG. 2 is a sectional view taken along line 2-2 of FIG. 1;

FIG. 3 is an exploded perspective view showing one of the carrier pins,the planet gear for that pin, and the bearing on which the planet gearrotates;

FIG. 4 is a perspective view partially broken away and in section ofanother epicyclic gear system constructed in accordance with andembodying the present invention; and

FIG. 5 is another perspective view, partially broken away and insection, of the epicyclic gear system shown in FIG. 4.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring now to the drawings, epicyclic gear systems A and B, each ofwhich is organized about a center axis X, have the traditional sun andring gears together with planet gears, but the planet gears in numberexceed those found in more conventional epicyclic systems, While thesystems A and B occupy little space, they have the capacity to transfertorque of a relatively high magnitude. Each system has a carrier towhich its planet gears are coupled through flexible pins in a doublecantilever arrangement. The pins establish offset axes Y about which theplanet gears rotate, and the axes Y closely parallel the center axis X,thus producing a good mesh between the planet and ring gears so as tohave a good load distribution across each planet gear and a generallyuniform load distribution among the several planet gears. The totalcross-sectional area of the pins is high to provide the shear area andsection modulus required to withstand the transfer of substantialtorque.

Turning now to the epicyclic gear system A (FIG. 1), it includes a sungear 2, a ring gear 4 located around the sun gear 2, and planet gears 6and 8 located in two rows between the sun gear 2 and ring gear 4, withplanet gears 6 occupying one row and the planet gears 8 occupying theother row. Moreover, the planet gears 6 are staggered with respect tothe planet gears 8, that is to say, they are offset circumferentially.Thus, the peripheries of the gears 6 may overlap the peripheries of thegears 8 without interference between the gears 6 and 8, this by reasonof the gears 6 and 8 being organized in the two rows. All the gears 2,4, 6 and 8 have teeth, and the planet gears 6 and 8 mesh with sun gear 2and ring gear 4 along the teeth of those gears 2, 4, 6 and 8.

In addition, the system A has a carrier 10 to which the planet gears 6and 8 are coupled, so that the planet gears 6 and 8 do not displaceaxially and interfere with each other or migrate out of the annularspace between the sun gear 2 and ring gear 4. The sun gear 2, ring gear4, and carrier 10 represent components of the system A at which powermay be supplied to the system A and delivered from the system A.

The carrier 10 includes (FIG. 1) a single flange 14 which lies adjacentto the row of planet gears 6, yet beyond the ends of those planet gears6 and beyond the ends of the sun gear 2 and ring gear 4 as well. Theflange 14 contains bores 16 which are arranged at equal circumferentialintervals and at equal radii from the center axis X. Fitted to the bores16 are short pins 20 and long pins 22, with the pins 20 and 22alternating. Thus, every other bore 16 contains a short pin 20, and theremaining bores 22 contain long pins 22. The pins 20 and 22 project fromthe flange 14 into the annular space between the sun gear 2 and ringgear 4 in the form of a cantilevers which give the pins 20 and 22 ameasure of flexibility. The gears 6 of the inner row rotate about theshort pins 20, whereas the gears 8 of the outer row rotate about thelong pins 22.

Each pin 20 has (FIGS. 2 & 3) a shank 26 at its fixed end where it isanchored in the flange 10 and at its free end a head 28. Between theshank 26 and head 28 the pin 20 may also have a groove 30 to enhance theflexibility of the pin 20. The shank 26 extends out of one of the bores16 of the flange 10 and into the planet gear 6 for the pin 20. The head28 also has a cylindrical surface of uniform diameter, and that diametermay be slightly greater than the diameter of the shank 26. While thehead 28 may be somewhat shorter than the shank 26, it still is longenough to lie partially within its planet gear 6.

The planet gears 6 rotate around their respective carrier pins 20 onantifriction bearings 34 (FIGS. 2 & 3), each lying within its gear 6 andaround its pin 20. Actually, each bearing 34 utilizes its planet gear 6as its outer race, in that the gear 6, itself, has two tapered raceways36 that are presented inwardly toward the axis Y of rotation for thegear 6 and taper downwardly toward each other. Each bearing 34 alsoincludes (FIG. 2) an inner race in the form of a unitary race sleeve 38and a separately formed rib ring 40 at one of the sleeve 38. The racesleeve 38 has a through bore 42, which at its one end receives theenlarged head 28 on the pin 20. An interference fit exists between thehead 28 and the surface of the bore 42 in the sleeve 38, but even so,head 28 of the sleeve 38 and the head 28 are joined together along acircular weld 44. Beyond the head 28 the surface of the bore 44 isspaced from the shank 26 of the pin 20, thus creating the secondcantilever. The sleeve 38 projects through the interior of the planetgear 6, and here is provided with two tapered raceways 46 which taperdownwardly toward each other and are presented outwardly toward theraceways 36 in the planet gear 6. The raceway 46 toward the free end ofthe race sleeve 38 leads up to a thrust rib 48 which is formed as anintegral part of the sleeve 38. The other raceway 46 at its large endleads into a rabbet 50 at the mounted end of the sleeve 38. The rib ring40 fits into the rabbet 50 and is secured to the sleeve 38 at anotherweld 52 to provide a rib at the large end of the adjoining raceway 46.

The bearing 34 also has (FIGS. 2 & 3) tapered rollers 54 arranged in tworows between the tapered raceways 36 of the planet gear 38 and thetapered raceways 46 on the race sleeve 38. The large end faces of therollers 54 in one row move along and are confined by the rib ring 40 onthe race sleeve 38, while the large ends of the rollers 54 in the otherrow move along and are confined by the integral thrust rib 48. By virtueof the position in which the rib ring 40 is secured to the race sleeve,38, the bearing 34 is in a condition of slight preload, so no clearancesexist between the raceways 36 and 46 and the rollers 54. Moreover, therollers 54 of the two rows are on apex, meaning that the conicalenvelopes in which their side faces lie have their apices at a commonpoint along the axis Y for planet gear 6.

U.S. patent application Ser. No. 10/680,043 of G. Fox and E. Jallat,filed Oct. 7, 2003, and entitled “Epicyclic Gear System”, describes thebearing 34 in more detail, and that application is incorporated hereinby reference. The pins 22 are similar to the pins 20, except that theirshanks 26 are longer. The planet gears 8 rotate on similar bearings 34located around those pins 22.

The grooves 30 between the shanks 26 and the heads 28 of the pins 20 and22 impart a measure of flexibility to the pins 20 at 22, butirrespective of whether the pins 20 and 22 have grooves 30, they shouldflex such that the axes Y of the planet gears 6 and 8 lie generallyparallel to the axis X. This insures that the planet gears 6 and 8 meshproperly with the sun gear 2 and ring gear 4 and that loads aredistributed evenly across the widths of the planet gears 6 and 8 anduniformly between the planet gears 6 and 8.

In the operation of the epicyclic gear system A the planet gears 6 and 8of the two rows transfer torque and power between the sun gear 2 andring gear 4. By reason of their increased number, the planet gears 6 and8 individually have less width than their counterparts in moretraditional epicyclic systems. Should they skew, the skewing will haveless detrimental effects than had the skewing occured with wider andmore conventional planet gears. Indeed, this extends the life of theplanet gears 6 and 8 and their bearings 34, as well as the lives of thesun gear 2 and ring gear 4. It also enables the entire gear system A tobe highly compact—all without compromising the cross sectional area ofthe flexible carrier pins 20 and 22. The staggered arrangement of theplanet gears 6 and 8 in two rows permits more planet gears and anincrease in the total cross-sectional area for the pins 20 and 22,particularly at the flange 14 of the carrier 10 where moments aregreatest.

The epicyclic gear system B (FIGS. 4 & 5) likewise has a sun gear 62, aring gear 64, and planet gears 66 and 68 located in two rows between thesun gear 62 and ring gear 64, with the gears 66 being in one row and thegears 68 being in the other row. Moreover, the planet gears 66 and 68are coupled to a carrier 70 which defines the axes Y about which theplanet gears 66 and 68 rotate.

In contrast to the carrier 10 for the epicyclic gear system A, thecarrier 70 for the system B has two flanges 72 and 74, the former beingadjacent to the planet gears 66 and the latter being adjacent to theplanet gears 68. The two flanges 72 and 74 are connected by bridges 76which extend between them, and in that sense the carrier 70 resembles astraddle carrier.

The gears 66 rotate around the pins 80 that are anchored in the flange72, whereas the gears 68 rotate on pins 82 that are anchored in theflange 74. For every pin 80 that projects from the flange 72, a pin 82projects from the flange 74, and while corresponding pins 80 and 82align, they are not connected. Thus each pin 80 or 82 is free to flexrelative to any other pin 80 or 82 including the pin 80 or 82 with whichit aligns. The pins 80 and 82 resemble the short pins 20 of the carrier10 for the planetary system A. Moreover the planetary gears 66 and 68rotate on bearings 84 similar to the bearings 34, including race sleeves38 which provide a double cantilever.

In the epicyclic system B, with its opposed planet gear arrangement, itis more likely that the deflection characteristics of each of flexiblepins 66 and 68 can have the same torque characteristics. However, theentire epicyclical arrangement will wind up from input to output sidewhen torque is applied to or taken from the carrier 70. So care must betaken to profile the teeth of the planetary gears 66 and 68 according tothe nominal wind up at each of their design mesh points.

In both the gear systems A and B the rolling elements of the bearings 34and 84 need not be tapered rollers, but may assume other shapes such asballs, cylindrical or spherical rollers, or needles. Indeed, thebearings need not contain rolling elements at all. Instead, each racesleeve 38 itself may function as a journal for the planet gear 6, 8, 66or 68 that is around it. When the bearings 34 and 84 have rollingelements, the raceways 36 and 46 may be on races that are formedseparately from the planet gears 6, 8, 66 and 68, on one hand, and therace sleeves 38, on the other.

1. An epicyclic gear system comprising: a sun gear; a ring gear locatedaround the sun gear; first planet gears located between and engaged withthe sun and ring gears in a first row; second planet gears locatedbetween and engaged with the sun and ring gears in a second row, withthe second gears being displaced axially from the first gears; and acarrier having first pins on which the first planet gears rotate andsecond pins on which the second planet gears rotate, the first andsecond pins being cantilevered from the carrier and being detached fromeach other.
 2. A gear system according to claim 1 wherein each pinprovides a double cantilevered mounting for the planet gear whichrotates on it.
 3. A gear system according to claim 1 wherein the carrierhas a single flange and the first and second pins are anchored in andextend from the flange such that they are cantilevered from the flange.4. A gear system according to claim 3 wherein the planet gears revolveabout their respective pins on bearings, with each bearing including arace sleeve which extends through the planet gear and over the pin, thesleeve being anchored to its pin remote from the flange and beingdirected toward the flange and through the planet gear from where it isanchored, whereby the planet gear is mounted on the carrier through adouble cantilever.
 5. A gear system according to claim 4 wherein thefirst and second pins are organized alternately in a circular row on theflange of the carrier, and the second pins are located between the firstplanet gears.
 6. A gear system according to claim 1, wherein the carrierhas first and second flanges, with the first flange being locatedadjacent to the first planet gears and the second flange being locatedadjacent to the second planet gears; and wherein the first pins extendfrom the first flange and the second pins extend from the second flange.7. A gear system according to claim 6 wherein the first and second pinsare cantilevered from the first and second flanges, respectively, of thecarrier; and wherein the planet gears revolve about their respectivepins on bearings, with each bearing including a race sleeve whichextends through the planet gear and over the pin, the sleeve beinganchored to its pin remote from the flange and being directed toward theflange and through the planet gear from where it is anchored, wherebythe planet gear is mounted on the carrier through a double cantilever.8. A gear system according to claim 7 wherein each first pin alignsaxially with a different second pin.
 9. A gear system according to claim8 wherein the carrier also has bridges connecting the first and secondflanges.
 10. An epicyclic gear system comprising: a sun gear; a ringgear located around the sun gear; first planet gears located in a rowbetween the sun and ring gears and being engaged with the sun and ringgears; and second planet gears located in another row between the sunand ring gears and being engaged with the sun and ring gears; a carrierhaving a single flange and first and second pins anchored in andprojecting from the flange, with the first pins projecting into thefirst planet gears so that the first gears revolve about the first pinsand the second pins projecting into the second planet gears so that thesecond gears revolve about the second pins, the first and second pinsbeing cantilevered from the flange of the carrier and being detachedfrom each other.
 11. A gear system according to claim 10 and wherein theplanet gears revolve about their respective pins on bearings, with eachbearing including a race sleeve which extends through the planet gearand over the pin, the sleeve being anchored to its pin remote from theflange and being directed toward the flange and through the planet gearfrom where it is anchored, whereby the planet gear is mounted on thecarrier through a double cantilever.
 12. A gear system according toclaim 11 wherein the first and second pins alternate and the second pinsextend between the first planet gears.
 13. A gear system according toclaim 11 wherein each bearing includes rolling elements located betweenthe race sleeve and the planet gear that is around the race sleeve. 14.A gear system according to claim 10 wherein the second pins are longerthan the first pins.
 15. An epicyclic gear system comprising: a sungear; a ring gear located around the sun gear; first planet gearslocated in a row between the sun and ring gears and being engaged withthe sun and ring gears; second planet gears located in another rowbetween the sun and ring gears and being engaged with the sun and ringgears; and a carrier having a first flange located adjacent to the firstplanet gears and a second flange located adjacent to the second planetgears and further having first pins cantilevered from the first flangeand extended into the first gears and second pins cantilevered from thesecond flange and extended into the second gears, all such that thefirst gears rotate about the first pins and the second gears rotateabout the second pins, the first and second pins being detached fromeach other.
 16. A gear system according to claim 15 wherein the planetgears revolve about there respective pins on bearings, with each bearingincluding a race sleeve which extends through the planet gear and overthe pin, the sleeve being anchored to its pin remote from the flange andbeing directed toward the flange for its pin and through the planet gearfrom where it is anchored, whereby the planet gear is mounted on thecarrier through a double cantilever.
 17. A gear system according toclaim 16 wherein each bearing includes rolling elements located betweenits race sleeve and the planet gear that is around the race sleeve. 18.A gear system according to claim 15 wherein each first pin alignsaxially with a different second pin, so the first and second planetgears are arranged in pairs.
 19. A gear system according to claim 18wherein the carrier also has bridges which connect the first and secondflanges and extend between adjacent pairs of first and second planetgears.